FACTORS INFLUENCING PREDATION OF THE WATERBUGS SPHAERODEMA-ANNULATUM (FAB) AND S-RUSTICUM (FAB) ON THE DISEASE TRANSMITTING SNAIL LYMNAEA (RADIX) LUTEOLA (LAMARCK)

Variations in the rate of predation of the waterbugs Sphaerodema annul atum and S. rusticum on the snails Lymnaea (Radix) luteola have been n oted in respect to the morphs of the waterbugs, size of the prey indiv iduals, densities of prey and predators, temperature and surface area of the waterbody concerned and the seasons. Consumption rate was highe st (7.2 and 2.2 individuals per day per individual of s. annulatum and S. rusticum, respectively) in prereproductive ages of the waterbugs. This was followed by a gradual decline with the increase in age of the predators. The consumption rate was gradually higher with the increas e of temperature from 20 degrees C to 35 degrees C. The bugs failed to survive beyond 35 days at 35 degrees C. Though the bugs prey upon the snails of all sizes preference for 6.5 x 4.5 mm to 8 x 5 mm individua ls by S. annulatum and for 5 x 3 mm to 6.5 x 4.5 mm individuals by S. rusticum is established. The waterbugs, irrespective of species, consu med the snail individuals belonged to 3 x 2 - 4 x 3 mm size group maxi mum when supplied separately. The rate of predation gradually declined with the rise of predator's density irrespective of waterbug species. Predation rate increased with increasing prey density. This was level off when the prey snails were 1100 and 700 in number for S. annulatum and S. rusticum respectively. An adult S. annulatum and S. rusticum c onsumed 5.04, 3.7, 1.43 and 3.36, 2.49, 1.04 snails per day respective ly in summer, monsoon and winter.